Epicyclic gear train

ABSTRACT

A gas turbine engine according to an example of the present disclosure includes, among other things, a propulsor section including a propulsor supported on a propulsor shaft, a turbine section including a turbine shaft, a compressor section having a plurality of compressor hubs with blades driven by the turbine shaft about an engine axis, and an epicyclic gear train interconnecting the propulsor shaft and the turbine shaft. The epicyclic gear train includes a sun gear coupled to the turbine shaft, intermediary gears arranged circumferentially about and meshing with the sun gear, a carrier and a ring gear including first and second portions. The first and second portions have axially opposed faces abutting one another at a radial interface.

CROSS REFERENCE TO RELATED APPLICATIONS

The present disclosure is a continuation of U.S. patent application Ser.No. 17/711,177 filed Apr. 1, 2022, which is a continuation of U.S.patent application Ser. No. 17/145,766 filed Jan. 11, 2021, which is acontinuation of U.S. patent application Ser. No. 16/805,917 filed Mar.2, 2020, which is a continuation of U.S. patent application Ser. No.15/984,494, filed May 21, 2018, now U.S. Pat. No. 10,577,965 grantedMar. 3, 2020, which is a continuation of U.S. patent application Ser.No. 14/824,351, filed Aug. 12, 2015, now U.S. Pat. No. 9,976,437,granted May 22, 2018, which is a continuation-in-part of U.S. patentapplication Ser. No. 13/486,766, filed Jun. 1, 2012, which is acontinuation of U.S. patent application Ser. No. 13/340,735, filed Dec.30, 2011, now U.S. Pat. No. 8,708,863, granted Apr. 29, 2014, which is acontinuation-in-part of U.S. patent application Ser. No. 11/504,220,filed Aug. 15, 2006, now U.S. Pat. No. 8,753,243, granted Jun. 17, 2014.

BACKGROUND OF THE INVENTION

This invention relates to a ring gear used in an epicyclic gear train ofa gas turbine engine.

Gas turbine engines typically employ an epicyclic gear train connectedto the turbine section of the engine, which is used to drive the turbofan. In a typical epicyclic gear train, a sun gear receives rotationalinput from a turbine shaft through a compressor shaft. A carriersupports intermediate gears that surround and mesh with the sun gear. Aring gear surrounds and meshes with the intermediate gears. Inarrangements in which the carrier is fixed against rotation, theintermediate gears are referred to as “star” gears and the ring gear iscoupled to an output shaft that supports the turbo fan.

Typically, the ring gear is connected to the turbo fan shaft using aspline ring. The spline ring is secured to a flange of the turbo fanshaft using circumferentially arranged bolts. The spline ring includessplines opposite the flange that supports a splined outercircumferential surface of the ring gear. The ring gear typicallyincludes first and second portions that provide teeth facing in oppositedirections, which mesh with complimentary oppositely facing teeth of thestar gears.

An epicyclic gear train must share the load between the gears within thesystem. As a result, the splined connection between the ring gear andspline ring is subject to wear under high loads and deflection. Sincethe spline connection requires radial clearance, it is difficult to geta repeatable balance of the turbo fan assembly. Balance can alsodeteriorate over time with spline wear.

SUMMARY OF THE INVENTION

In a featured embodiment, a turbine engine has a fan shaft. At least onetapered bearing is mounted on the fan shaft. The fan shaft includes atleast one passage extending in a direction having at least a radialcomponent, and adjacent the at least one tapered bearing. A fan ismounted for rotation on the tapered bearing. An epicyclic gear train iscoupled to drive the fan. The epicyclic gear train includes a carriersupporting intermediate gears that mesh with a sun gear. A ring gearsurrounds and meshes with the intermediate gears. Each of theintermediate gears are supported on a respective journal bearing. Theepicyclic gear train defines a gear reduction ratio of greater than orequal to about 2.3. A turbine section is coupled to drive the fanthrough the epicyclic gear train. The turbine section has a fan driveturbine that includes a pressure ratio that is greater than about 5. Thefan includes a pressure ratio that is less than about 1.45, and the fanhas a bypass ratio of greater than about ten (10).

In another embodiment according to the previous embodiment, the fanshaft is coupled to the ring gear.

In another embodiment according to any of the previous embodiments, theat least one tapered bearing includes a first tapered bearing and the atleast one passage includes a first passage and a second passage. Thefirst passage is located at an axially forward side of the first taperedbearing and the second passage is located at an axially aft side of thefirst tapered bearing.

In another embodiment according to any of the previous embodiments, thefan shaft includes, on a radially inner surface, at least one wellextending between axial sides and a radial side, and the at least onepassage opens at the radial side.

In another embodiment according to any of the previous embodiments, thefan shaft includes, on a radially inner surface, a plurality of wellseach extending between axial side walls and a radial side wall, and theat least one passage includes a plurality of passages that open atrespective ones of the radial side walls of the plurality of wells.

In another embodiment according to any of the previous embodiments, twowells of the plurality of wells are axially adjacent such that the twowells share a common axial side wall.

In another embodiment according to any of the previous embodiments, theaxial side walls are gradually sloped.

In another embodiment according to any of the previous embodiments, theepicyclic gear train has a gear reduction ratio of greater than or equalto 2.3.

In another embodiment according to any of the previous embodiments, theepicyclic gear train has a gear reduction ratio of greater than or equalto about 2.5.

In another embodiment according to any of the previous embodiments, theepicyclic gear train has a gear reduction ratio of greater than or equalto 2.5.

In another embodiment according to any of the previous embodiments, thefan defines a bypass ratio of greater than about 10.5:1 with regard to abypass airflow and a core airflow.

In another embodiment according to any of the previous embodiments,there are three turbines, with the fan drive turbine being a lowestpressure turbine, and there being a high pressure turbine and anintermediate pressure turbine, with the high pressure turbine and theintermediate pressure turbine each driving a compressor rotor.

Although different examples have the specific components shown in theillustrations, embodiments of this invention are not limited to thoseparticular combinations. It is possible to use some of the components orfeatures from one of the examples in combination with features orcomponents of another of the examples.

These and other features disclosed herein can be best understood fromthe following specification and drawings, the following of which is abrief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional view of a front portion of a gasturbine engine illustrating a turbo fan, epicyclic gear train and acompressor section.

FIG. 2 is an enlarged cross-sectional view of the epicyclic gear trainshown in FIG. 1 .

FIG. 3 is an enlarged cross-sectional view of an example ring gearsimilar to the arrangement shown in FIG. 2 .

FIG. 4 is a view of the ring gear shown in FIG. 3 viewed in a directionthat faces the teeth of the ring gear in FIG. 3 .

FIG. 5 shows another embodiment.

FIG. 6 shows yet another embodiment.

DETAILED DESCRIPTION

A portion of a gas turbine engine 10 is shown schematically in FIG. 1 .The turbine engine 10 includes a fixed housing 12 that is constructedfrom numerous pieces secured to one another. A compressor section 14having compressor hubs 16 with blades are driven by a turbine shaft 25about an axis A. A turbo fan 18 is supported on a turbo fan shaft 20that is driven by a compressor shaft 24, which supports the compressorhubs 16, through an epicyclic gear train 22.

In the example arrangement shown, the epicyclic gear train 22 is a stargear train. Referring to FIG. 2 , the epicyclic gear train 22 includes asun gear 30 that is connected to the compressor shaft 24, which providesrotational input, by a splined connection. A carrier 26 is fixed to thehousing 12 by a torque frame 28 using fingers (not shown) known in theart. The carrier 26 supports star gears 32 using journal bearings 34that are coupled to the sun gear 30 by meshed interfaces between theteeth of sun and star gears 30, 32. Multiple star gears 32 are arrangedcircumferentially about the sun gear 30. Retainers 36 retain the journalbearings 34 to the carrier 26. A ring gear 38 surrounds the carrier 26and is coupled to the star gears 32 by meshed interfaces. The ring gear38, which provides rotational output, is secured to the turbo fan shaft20 by circumferentially arranged fastening elements, which are describedin more detail below.

As shown, each of the star gears 32 is supported on one of the journalbearings 34. Each journal bearing 34 has an internal central cavity 34 athat extends between axial ends 35 a and 35 b. In this example, asshown, the internal central cavity 34 a is axially blind in that theaxial end 35 a is closed. At least one passage 37 extends from theinternal central cavity 34 a to a peripheral journal surface 39. In theexample, the at least one passage 37 includes a first passage 37 a and asecond passage 37 b that is axially spaced from the first passage 37 a.As shown, the first and second passages 37 a and 37 a are non-uniformlyspaced with regard to the axial ends 35 a and 35 b of the internalcentral cavity 34 a.

In operation, lubricant is provided to the internal central cavity 34 a.The lubricant flows through the internal central cavity 34 a and thenoutwardly through the at least one passage 37 to the peripheral journalsurface 39. The arrangement of the internal central cavity 34 a and atleast one passage 37 thereby serves to cool and lubricate the journalbearing 32.

The gas turbine engine 10 is a high-bypass geared architecture aircraftengine. In one disclosed, non-limiting embodiment, the engine 10 has abypass ratio that is greater than about six (6) to ten (10), theepicyclic gear train 22 is a planetary gear system or other gear systemwith a gear reduction ratio of greater than about 2.3 or greater thanabout 2.5, and a low pressure turbine of the engine 10 has a pressureratio that is greater than about 5. In one disclosed embodiment, theengine 10 bypass ratio is greater than about ten (10:1) or greater thanabout 10.5:1, the turbofan 18 diameter is significantly larger than thatof the low pressure compressor of the compressor section 14, and the lowpressure turbine has a pressure ratio that is greater than about 5:1. Inone example, the epicyclic gear train 22 has a gear reduction ratio ofgreater than about 2.3:1 or greater than about 2.5:1. It should beunderstood, however, that the above parameters are only exemplary of oneembodiment of a geared architecture engine and that the presentinvention is applicable to other gas turbine engines including directdrive turbofans.

A significant amount of thrust is provided by a bypass flow B due to thehigh bypass ratio. The fan 18 of the engine 10 is designed for aparticular flight condition—typically cruise at about 0.8 M and about35,000 feet. The flight condition of 0.8 M and 35,000 ft, with theengine at its best fuel consumption—also known as “bucket cruiseTSFC”—is the industry standard parameter of lbm of fuel being burneddivided by lbf of thrust the engine produces at that minimum point. “Lowfan pressure ratio” is the pressure ratio across the fan blade alone.The low fan pressure ratio as disclosed herein according to onenon-limiting embodiment is less than about 1.45. “Low corrected fan tipspeed” is the actual fan tip speed in ft/sec divided by an industrystandard temperature correction of [(Tambient deg R)/518.7){circumflexover ( )}0.5]. The “Low corrected fan tip speed” as disclosed hereinaccording to one non-limiting embodiment is less than about 1150ft/second.

Referring to FIGS. 3 and 4 , the ring gear 38 is a two-piececonstruction having first and second portions 40, 42. The first andsecond portions 40, 42 abut one another at a radial interface 45. Atrough 41 separates oppositely angled teeth 43 (best shown in FIG. 4 )on each of the first and second portions 40, 42. The arrangement ofteeth 43 forces the first and second portions 40, 42 toward one anotherat the radial interface 45. The back side of the first and secondportions 40, 42 includes a generally S-shaped outer circumferentialsurface 47 that, coupled with a change in thickness, provides structuralrigidity and resistance to overturning moments. The first and secondportions 40, 42 have a first thickness T1 that is less than a secondthickness T2 arranged axially inwardly from the first thickness T1. Thefirst and second portions 40, 42 include facing recesses 44 that form aninternal annular cavity 46.

The first and second portions 40, 42 include flanges 51 that extendradially outward away from the teeth 43. The turbo fan shaft 20 includesa radially outwardly extending flange 70 that is secured to the flanges51 by circumferentially arranged bolts 52 and nuts 54, which axiallyconstrain and affix the turbo fan shaft 20 and ring gear 38 relative toone another. Thus, the spline ring is eliminated, which also reducesheat generated from windage and churning that resulted from the sharpedges and surface area of the splines. The turbo fan shaft 20 and ringgear 38 can be rotationally balanced with one another since radialmovement resulting from the use of splines is eliminated. An oil baffle68 is also secured to the flanges 51, 70 and balanced with the assembly.

Seals 56 having knife edges 58 are secured to the flanges 51, 70. Thefirst and second portions 40, 42 have grooves 48 at the radial interface45 that form a hole 50, which expels oil through the ring gear 38 to agutter 60 that is secured to the carrier 26 with fasteners 61 (FIG. 2 ).The direct radial flow path provided by the grooves 48 reduces windageand churning by avoiding the axial flow path change that existed withsplines. That is, the oil had to flow radially and then axially to exitthrough the spline interface. The gutter 60 is constructed from a softmaterial such as aluminum so that the knife edges 58, which areconstructed from steel, can cut into the aluminum if they interfere.Referring to FIG. 3 , the seals 56 also include oil return passages 62provided by first and second slots 64 in the seals 56, which permit oilon either side of the ring gear 38 to drain into the gutter 60. In theexample shown in FIG. 2 , the first and second slots 64, 66 are insteadprovided in the flange 70 and oil baffle 68, respectively.

FIG. 5 shows an embodiment 200, wherein there is a fan drive turbine 208driving a shaft 206 to in turn drive a fan rotor 202. A gear reduction204 may be positioned between the fan drive turbine 208 and the fanrotor 202. This gear reduction 204 may be structured and operate likethe gear reduction disclosed above. A compressor rotor 210 is driven byan intermediate pressure turbine 212, and a second stage compressorrotor 214 is driven by a turbine rotor 216. A combustion section 218 ispositioned intermediate the compressor rotor 214 and the turbine section216.

FIG. 6 shows yet another embodiment 300 wherein a fan rotor 302 and afirst stage compressor 304 rotate at a common speed. The gear reduction306 (which may be structured as disclosed above) is intermediate thecompressor rotor 304 and a shaft 308 which is driven by a low pressureturbine section.

Although embodiments of this invention have been disclosed, a worker ofordinary skill in this art would recognize that certain modificationswould come within the scope of this invention. For that reason, thefollowing claims should be studied to determine the true scope andcontent of this invention.

What is claimed is:
 1. A gas turbine engine comprising: a propulsorsection including a propulsor supported on a propulsor shaft; a turbinesection including a turbine shaft; a compressor section having aplurality of compressor hubs with blades driven by the turbine shaftabout an engine axis; and an epicyclic gear train interconnecting thepropulsor shaft and the turbine shaft, the epicyclic gear traincomprising: a sun gear coupled to the turbine shaft; intermediary gearsarranged circumferentially about and meshing with the sun gear; acarrier and support means for supporting each of the intermediate gearsrelative to the carrier; and a ring gear including first and secondportions, the first and second portions each having an inner peripherywith teeth intermeshing with the intermediate gears, the first andsecond portions having axially opposed faces abutting one another at aradial interface, the first and second portions including respectiveflanges extending along the radial interface radially outward from theteeth, and the ring gear including discharge means for expellinglubricant from the radial interface outwardly of the ring gear.
 2. Thegas turbine engine as recited in claim 1, wherein the epicyclic geartrain defines a gear reduction ratio of greater than or equal to 2.5. 3.The gas turbine engine as recited in claim 2, wherein the epicyclic geartrain is a planetary gear system.
 4. The gas turbine engine as recitedin claim 2, wherein the ring gear includes attachment means for securingthe first and second portions of the ring gear to the propulsor shaft.5. The gas turbine engine as recited in claim 2, wherein the ring gearincludes engagement means for forcing the first portion and the secondportion toward one another at the radial interface.
 6. The gas turbineengine as recited in claim 5, wherein the first and second portions ofthe gear train includes means for resisting overturning moments.
 7. Thegas turbine engine as recited in claim 2, wherein the ring gear includesaccumulation means for capturing lubrication expelled toward the radialinterface.
 8. The gas turbine engine as recited in claim 2, wherein thesupport means includes journal bearings that support the respectiveintermediate gears, and each journal bearing includes lubrication meansfor conveying lubricant through the journal bearing to a peripheraljournal surface of the journal bearing.
 9. The gas turbine engine asrecited in claim 2, wherein the gear train includes a torque framehaving securement means for fixing the carrier to a fixed housing. 10.The gas turbine engine as recited in claim 2, wherein: the gear trainincludes collection means for receiving lubricant expelled by thedischarge means through the radial interface; the discharge meansinhibits an axial flow of lubricant passing along the radial interfaceprior to being expelled toward the collection means; and the gear trainincludes return means for communicating lubricant from an outerperiphery of the respective first and second portions of the ring gearoutwardly to the collection means.
 11. The gas turbine engine as recitedin claim 2, further comprising: an input shaft that interconnects thesun gear and the turbine shaft, the input shaft including an undulationthat extends radially outward relative to the engine axis.
 12. The gasturbine engine as recited in claim 2, wherein the gear train includeslubrication means for conveying lubricant from a periphery of theintermediate gears to the radial interface.
 13. The gas turbine engineas recited in claim 2, wherein the propulsor is a turbo fan, and thepropulsor shaft is a fan shaft supporting the fan.
 14. The gas turbineengine as recited in claim 13, further comprising a bypass ratio ofgreater than 10.5 and a low corrected fan tip speed of less than 1150ft/second, wherein the fan includes a pressure ratio of less than 1.45across the fan blade alone at cruise at 0.8 M and 35,000 feet.
 15. Thegas turbine engine as recited in claim 14, wherein the ring gearincludes engagement means for forcing the first portion and the secondportion toward one another at the radial interface.
 16. The gas turbineengine as recited in claim 15, wherein the ring gear includes attachmentmeans for securing the first and second portions of the ring gear to thefan shaft.
 17. The gas turbine engine as recited in claim 16, whereinthe gear train includes collection means for receiving lubricantexpelled by the discharge means through the radial interface, and thering gear includes accumulation means for capturing lubrication expelledtoward the radial interface.
 18. The gas turbine engine as recited inclaim 17, wherein the gear train includes return means for communicatinglubricant from an outer periphery of the respective first and secondportions of the ring gear outwardly to the collection means.
 19. The gasturbine engine as recited in claim 18, further comprising: a splitterthat defines an entrance to the compressor section; and wherein theradial interface of the ring gear is axially aft of the splitterrelative to the engine axis.
 20. The gas turbine engine as recited inclaim 14, wherein the epicyclic gear train is a planetary gear system.